Dynamic Supramolecular Polyurethane Elastomers Enabling Bioinspired Strain‐Adaptive Stiffening to Resolve the Softness–Strength Paradox

ABSTRACT The rapid progress of soft robotics and flexible electronics has sparked tremendous demand for elastomers that unite high mechanical strength with intrinsic softness, thereby mimicking the mechanical performance of natural skin. Herein, we report a class of dynamically crosslinked supramolecular polyurethanes that combine skin‐comparable low modulus with high strength and room‐temperature self‐healing, achieved through a segmental molecular engineering strategy. The design leverages entropy‐driven soft elasticity together with enthalpy‐governed strain‐stiffening and energy dissipation, dictated by polymer segment topology. Using a prototypical supramolecular elastomer, we demonstrate that incorporating an isophorone diisocyanate (IPDI) chain extender, whose steric configuration matches that of ureidopyimidinone (UPy), reinforces hydrogen bonding interaction and suppresses premature crystallization. The optimized elastomer exhibits an ultralow initial modulus (<3 MPa) yet undergoes pronounced strain‐stiffening, yielding exceptional tensile strength (>50 MPa) and high fracture toughness (∼2×10 ⁵ J m ⁻² ), outperforming state‐of‐the‐art room‐temperature self‐healing elastomers. Moreover, the elastomer features hydrophobicity, ensuring stability in underwater applications. These results underscore the promise of segment‐level molecular engineering for constructing dynamic polyurethanes with thermoplastic processability, skin‐like softness, and unprecedented mechanical robustness.